This invention relates, in general, to combination locks, and in particular, to an improvement consisting of a device for preventing unauthorized opening of the lock through illicit internal manipulation of the lock components.
Combination locks of the type to which this invention pertains commonly employ a plurality of gated tumbler wheel assemblies axially-disposed on the dial shaft of the lock. Exemplary of these tumbler wheel assemblies is that disclosed in U.S. Pat. No. 4,142,388 to Phillips, et al. Normally, these tumbler wheels are accesses for manipulation by the user by means of the dial shaft, which passes through the housing of the lock and is typically provided with a numbered dial wheel affixed to its outer extremity. By suitable manipulation of the dial wheel in a series of predetermined rotations, the user will cause the gates located in each of the tumbler wheel assemblies to arrive in an aligned position. It is only upon the occurrence of this circumstance that an arm or fence will fit into the gate, and, depending on the construction of the lock, cause a latch to open, or in some cases, upon further manipulation of the dial or separate mechanism, the lock bolt to be drawn.
In the latter type of lock, it is not uncommon for the lock to include a fence lever which is pivotally-attached to the bolt and having a cam-following nose part which rides upon a cam wheel mounted on the dial shaft. The fence lever is biased towards the cam wheel, which also has a gate in it, and, when the predetermined combination of numbers is dialed on the dial wheel, the gates of the tumbler wheel assemblies align, permitting the fence on the lever to fall into their gates which, in turn, permits the nose part of the lever to engage the cam wheel gate, and, upon further rotation of the dial shaft by the operator, the fence lever is caused to translate and withdraw the bolt.
It is common in these combination locks for the nose portion of the fence lever normally to ride on the outer periphery of the cam wheel so that the fence member associated with the fence lever will not ride upon the tumbler wheels of the lock mechanism. Typical of such locks is that shown in U.S. Pat. No. 4,142,388. It is desirable to avoid having the fence lever ride upon the tumbler wheel because experience has taught that persons skilled in illicit lock manipulation can develop a "feel" for the position of the tumbler wheel assemblies from vibrations sent through the combination dial shaft such that, given sufficient time and access to the lock, these persons may gain unauthorized entry into the area these locks are intended to protect.
Unfortunately, experience has also taught that the engagement between the nose portion of the fence lever and the gate of the cam wheel can also permit a skilled person to determine where the cam wheel gate is by "feel" and then by manipulating the lock parts in a predetermined manner, also bring the fence member in contact with the edges of the gates of the wheel assemblies while the lever nose is positioned in the cam wheel gate.
Various mechanisms have been utilized to overcome the contact or "feel" of the fence lever or the nose piece riding on the rotating lock portion which is typically accomplished by retaining the fence lever in a position away from the rotating components until such point in the manipulation of the lock as it becomes desirable to have the fence lever engage within the gate of the tumbler wheels on the cam wheel. Such devices are disclosed in U.S. Pat. No. 3,991,596 and a co-pending application, Ser. No. 676,628 filed Nov. 30, 1984.
Unfortunately, experience has taught that persons confronted with such locks and possessed of a strong desire to achieve access to the contents of areas protected by these locks, but lacking the wherewithall to do so, will resort to extraordinary unauthorized access means. For example, it has been demonstrated that, given sufficient access to the lock, the combination dial can be removed from the dial shaft by the application of sufficient force, such as that applied with a sledge hammer. With the dial shaft thus exposed, a blow can then be struck to the shaft in the direction of its axis which, of sufficient magnitude, will expel the dial shaft through the rear of the lock's housing. The unauthorized manipulator can then, by means of insertion of one or more hook-shaped fishing wires through the dial shaft bore, manipulate the gates of the tumbler wheels into alignment and/or activate the fence lever.
Similarly, it has been demonstrated that an unauthorized lock manipulator can, by means of drilling into the front of the lock into the region of the housing immediately outside the circumference of the tumbler wheel assemblies, insert one or more hook-shaped "fishing" wires into the interior of the lock and, by suitable manipulation of the circumference of the tumbler wheel assemblies, gain illicit access.